This invention relates to a thin-film magnetic head and more particularly to a thin-film magnetic head having a magnetic film with a double step structure, and a method for fabricating the head.
A thin-film magnetic head is commonly fabricated by thin-film forming technique such as a vacuum evaporation or sputtering and a high precision patterning technique called photolithography. Such a common construction of the thin-film magnetic head is described in U.S. Pat. No. 4,219,853. It is described in U.S. Pat. No. 4,190,872 that in such a thin-film magnetic head, in order to enhance the conversion efficiency of the magnetic head as well as to boost resolution for reproducing and to relax a magnetization saturation for recording, the thickness of a magnetic film must be varied at the side of each magnetic core opposed to a recording medium, i.e., a magnetic gap region and a back region of the core succeeding thereto--that is, such a double step structure must be adopted that the thickness of the film in the back region is greater than the thickness of the film in the magnetic gap region.
The magnetic core is ordinarily made by such a technique as vacuum evaporation plating and sputtering. The plating technique is advantageous in that it is relatively easy to form the above-mentioned shape or structure but disadvantageous in that the magnetic performance of the core greatly varies according to a slight variation of a plating condition, the magnetic head performance is not made stable and the control of the thickness of a magnetic film is difficult. On the other hand, the vacuum evaporation or sputtering is advantageous in that less amount of fluctuation in a magnetic film quality occurs and the film thickness is easily controlled in forming the film but disadvantageous in that the precision of film thickness is deteriorated when a stacked film is etched to form a magnetic core of the double step structure mentioned above. In other words, the magnetic core of a double step structure is made by the vacuum evaporation of sputtering through the following three processes such as shown in FIGS. 1A-1D, FIGS. 2A-2D and FIGS. 3A-3C. In the first process shown in FIGS. 1A-1D, a magnetic film 2 stacked on a substrate 1 is patterned to be a predetermined shape through wet or dry etching, a magnetic film 3 is further stacked on the resultant surface and thereafter etched away in a predetermined shape. In the second process shown in FIGS. 2A-2D, the magnetic film 3 is first formed and the magnetic film 2 of the FIGS. 1A-1D is subsequently formed thereon. In the third process shown in FIGS. 3A-3D, a relatively thick magnetic film 5 is stacked on a substrate 4, partially reduced by a predetermined thickness and thereafter etched away in a predetermined shape.
The first process has such a defect that the substrate (or under film), which will be exposed during the progress of etching the magnetic film 2, may be damaged. The fabricating process of a thin film magnetic head using this process is shown in FIGS. 4A-4D. First, as shown in FIG. 4A, a first magnetic film 12 is formed on a substrate 10 and is thereafter patterned in a predetermined shape. A second magnetic film 13 is formed on the first magnetic film 12. A magnetic gap film 14 is formed and thereafter an inter-layer insulating film 15 and a conductor coil 16 are successively formed. The inter-layer insulating film 15 is etched away in a predetermined shape. A first upper magnetic film 17 is formed on the resultant surface. Next, as shown in FIG. 4B, a front area of the first upper magnetic film 17 (magnetic gap area) is etched away by such a dry etching technique ion-milling. A second upper magnetic film 19 is formed on the resultant surface as shown in FIG. 4C. In the last step, the second upper magnetic film 19 is subjected to patterning as shown in FIG. 4D. Thus, there is obtained a thin film magnetic head of such a double step structure that the back region of the magnetic core is thicker than the magnetic gap region. However, in the process there occurs such an inconvenience that the film thickness of the magnetic gap film 14, which must be precisly defined, is caused to be reduced during the step of patterning the upper magnetic film 17 as shown in FIG. 4B. This inconvenience or drawback is remarkable where such a dry etching technique as ion-milling, which can particularly attain high precision etching, is employed. This is because wet etching is a chemical technique while dry etching is generally a physical technique and has a low selectivity of etching.
On the other hand, the second process has a drawback that the exposed portion of the magnetic film 3 will be etched to reduce the thickness thereof during the step of etching the magnetic film 2. The exposed portion of the magnetic film 3 is a portion which requires particularly precise film thickness definition among the portions of the magnetic core. The film thickness variation at this portion results in the fluctuation of the performance of the magnetic head. Further, the third process mentioned above has also the same drawback as the second process.
As described above, it has been conventionally difficult to implement a thin film magnetic head having a magnetic core of such a double step structure as to consist of a magnetic gap region of a given thickness and a back region successive thereto which is thicker than the magnetic gap area with good film thickness precision in the magnetic core and magnetic gap and excellent head performance.